Extravascular Implantable Cardioverter-Defibrillator Sensing and Detection in a Large Global Population.

BACKGROUND: The extravascular (EV) implantable cardioverter-defibrillator (ICD) includes features to address sensing and arrhythmia detection challenges presented by its substernal lead location. OBJECTIVES: In this study, the authors sought to evaluate sensing and detection performance in 299 patients discharged with an EV-ICD in the global pivotal study. METHODS: We reviewed and adjudicated all induced ventricular fibrillation (VF) episodes and spontaneous device-stored episodes that satisfied rate and duration criteria in a programmed ventricular tachycardia (VT)/VF therapy zone. RESULTS: At implantation, all EV-ICDs detected induced VF at the programmed sensitivity; 95.9% detected VF with a 3× safety margin. In follow-up, EV-ICDs detected all 59 VT/VF episodes that sustained until therapy. Of 1,034 non-VT/VF episodes, oversensing caused 87.9% and supraventricular tachycardia caused 12.1%. Therapy was withheld in 80.9%, aborted in 10.6%, and delivered in 8.5%. The most common causes of oversensing were myopotentials (61.2%) and P-wave oversensing (PWOS) (19.9%). Inappropriate shocks occurred in only 3.2% of myopotential episodes, but in 21.8% of PWOS episodes. Myopotential oversensing was more common with Ring-Can sensing (P < 0.0001) and correlated with low R-wave amplitude (P < 0.0001). PWOS occurred almost exclusively with Ring1-Ring2 sensing (P = 0.0001) and began with transient decrease in R-wave or increase in P-wave amplitude (P < 0.0001). In software emulation, a new PWOS discriminator significantly reduced total inappropriate detections. CONCLUSIONS: In a global population, EV-ICD detected induced and spontaneous VT/VF accurately. Although discriminators withheld detection from most non-VT/VF episodes, inappropriate shocks were common. The most common cause was PWOS, which may be reduced by optimizing sensing at implantation and incorporation of the PWOS discriminator, which is now in the current device. (Extravascular ICD Pivotal Study [EV ICD]; NCT04060680).

High amplitude T-wave alternans precedes spontaneous ventricular tachycardia or fibrillation in ICD electrograms.

BACKGROUND: T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or fibrillation (VF) in animal studies, suggesting that it may provide a warning for VT/VF in implantable cardioverter defibrillator (ICD) patients. Clinically, measurement of surface ECG TWA requires preprocessing the input signal to reduce noise and/or analyzing more sinus beats than are recorded in ICDs as pre-onset, stored intracardiac electrograms (EGMs) before VT/VF. Our objective was to measure TWA from the few sinus EGMs stored in ICDs before spontaneous VT/VF in humans. OBJECTIVE: The purpose of this study was to evaluate the technical feasibility of measuring TWA from pre-onset ICD EGMs and to measure EGM TWA before spontaneous VT/VF in humans. METHODS: We developed a method to measure EGM TWA as a simple average (AVE) of peak-to-peak alternans. Using simulation, we determined the effect of ICD signal processing on EGM TWA for durations comparable to those in pre-onset EGMs. We then applied this method to pre-onset ICD EGMs that preceded 101 episodes of sustained VT/VF in 10 patients. In 6 of these patients, EGM recordings in atrial pacing and sinus rhythm provided control data. RESULTS: In simulation, the AVE method discriminated input TWA differences > or = 15 microV. In patients, EGM TWA was 78 +/- 62 microV prior to VT/VF vs. 13 +/- 10 microV in control recordings (p< .0001). Eighty percent of pre-onset measurements exceeded 30 microV, while 95% of control measurements were less than 30 microV. CONCLUSIONS: A simple averaging method can measure TWA preceding VT/VF in stored ICD EGMs. Pilot data indicate that high-amplitude EGM TWA usually precedes spontaneous VT/VF and is infrequent in control recordings. They provide a rationale for developing ICD technology to measure EGM TWA continuously, both to warn patients and to initiate pacing algorithms to prevent VT/VF.

Detection of T-wave alternans using an implantable cardioverter-defibrillator.

BACKGROUND: Microvolt T-wave alternans (TWA) increases acutely prior to ventricular tachycardia (VT) or ventricular fibrillation (VF) in computer simulations and animal models, suggesting that TWA may provide a warning for VT/VF in patients with an implantable cardioverter-defibrillator (ICD). OBJECTIVES: The purposes of this study were to develop a method for analyzing TWA recorded from ICD electrograms (EGMs) and to evaluate the degree of concordance between EGM TWA and TWA recorded from the surface ECG. METHODS: We developed a software program to measure EGM TWA in the frequency domain and then used simulated EGMs to determine the effects of ICD signal processing, electrical noise, and variation in the EGM fiducial point on the recorded amplitude and K score (signal-to-noise ratio) of TWA. We then applied this method to analyze TWA simultaneously using both surface ECGs and ICD EGMs during incremental pacing in 25 ICD patients. Pacing modes and EGM sources were varied in repeated trials. EGMs with dynamic range adjusted to achieve a large T wave were telemetered to a digital Holter recorder and measured offline. ECG TWA was analyzed using a commercial system. A positive (+) ECG test had sustained alternans >or=1.9 microV with K score >or=3. Stored EGMs were reviewed for VT/VF during a 6-month follow-up period. RESULTS: Simulations demonstrated that the EGM method accurately identified TWA >or=10 microV. Overall, 10 (40%) patients had at least one ECG TWA+ test and 15 patients (60%) had no ECG TWA+ tests. The maximum value of TWA was greater in EGMs than in ECGs (median 64 microV vs 2.2 microV, P <.0001). EGM TWA was greater in ECG TWA+ tests than in ECG TWA- tests (169 +/- 175 microV vs 71 +/- 61 microV, P <.001). Using a sustained EGM TWA threshold of 30 microV, EGM TWA was concordant with ECG TWA in 63 (84%) of 75 analyzed tests (P <.0001) and predicted ECG TWA results with 85% sensitivity and 84% specificity. Both ECG and EGM TWA predicted VT/VF during follow-up (ECG: P = .006; EGM: P = .035). CONCLUSION: The amplitude of TWA is at least 10 times greater on ICD EGMs than on surface ECGs. EGM and ECG TWA have substantial concordance and comparable predictive value for spontaneous VT/VF. These observations support the hypothesis that ECG and EGM TWA detect the same electrical alternans phenomenon.